In a virtual circuit packet switch, a so-called virtual circuit connection needs to be established between a pair of data modules before the modules may exchange messages with one another. (The connection is virtual because the bandwidth of the intermodule transmission medium is used to transport data between the modules only when the modules have data to send. Otherwise, the transmission bandwidth may be used to send data for a different virtual connection that is established over the medium. Thus, the transmission is shared among a set of data modules). Such a virtual circuit connection is therefore defined by associated translation data comprising the modules' respective addresses and associated channel numbers. Such data is generated as a result of a call set-up procedure that is initiated by one of the data modules, and is stored in a translation memory referred to as the switch. The packet switch uses the translation data to route a message between the pair of modules by translating the contents of an associated address and channel field identifying the originator of the associated message into the address and channel number identifying the intended destination, in which, for virtual circuit service, the address-channel number pairs are unique across the modules on a packet switch. In this sense, the virtual circuit connection is selectively activated by virtue of the presence of the associated translation data.
A message which is transported via a virtual circuit connection is commonly referred to as a "connection oriented" message, which is unlike a so-called "connectionless" message. A connectionless message is a message that is transported on the "fly" and, therefore, is not preceded by a call set-up procedure involving the generation of associated translation data between specific modules. A connectionless message reaches its intended destination as a result of the originator inserting in the message the address of the destination and then having the switching and transmission mechanisms route the messages to the set of modules capable of receiving connectionless messages.
It can be appreciated from the foregoing that if the virtual circuit packet switch were presented with a connectionless message, then the switch would either misroute or discard the message. The reason for this is that the switch would not have in place the appropriate translation data defining a respective virtual circuit connection between the originator and destination of the connectionless message. Consequently, the inability to transport (route) connectionless messages limits the application of a virtual circuit packet switch to transporting just connection oriented messages.